TECHNICAL FIELD
[0001] The present invention relates to a vehicle control device, and more particularly
to a vehicle control device for controlling vehicle traveling.
BACKGROUND ART
[0002] In
JP 2006-218935A (Patent Document 1), a vehicle traveling support device is described. In this vehicle
traveling support device, while detecting an object in a traveling direction of an
own vehicle, it is predicted whether a safe distance is ensured at the time of closest
approach of the own vehicle to the detected object, wherein, when the safe distance
is predicted to fail to be ensured, traveling support control is executed. Further,
in this vehicle traveling support device, the orientation of the object is detected
to set the safe distance according to the detected orientation.
[0003] However, the control by the vehicle traveling support device described in Patent
Document 1 is merely aimed at avoiding collision. However, in a satiation where, during
normal traveling, the own vehicle passes by or overtakes a preceding vehicle (parked
vehicle), it is not enough to allow collision avoidance. That is, when passing by
or overtaking a preceding vehicle (parked vehicle), it is necessary to maintain, with
respect to the preceding vehicle (parked vehicle), a distance (clearance) enough to
avoid giving a driver a feeling of insecurity.
[0004] In order to achieve this necessity, the applicant has developed a vehicle control
device configured to set, around an object such as a preceding vehicle, a plurality
of speed limit distributions defining respective different permissible upper limit
relative speeds, and control the vehicle speed and/or steering of an own vehicle not
to exceed the upper limits (
PCT/JP2016/075233). By incorporating such a vehicle control device, it becomes possible to successfully
obtain vehicle control allowing the own vehicle to maintain a sufficient distance
(clearance) with respect to an object such as a preceding vehicle, even when the own
vehicle passes by and overtakes the object, thereby less likely to give a driver a
feeling of insecurity.
CITATION LIST
[Parent Document]
SUMMARY OF INVENTION
[Technical Problem]
[0006] However, a distance between an own vehicle and a preceding vehicle, at which a driver
feels safe and secure, is not always constant, but varies depending on the state of
a road surface on which the own vehicle is traveling. Thus, in a situation where the
own vehicle is controlled by a vehicle control device, such that a certain constant
distance is taken between the own vehicle and a preceding vehicle, the driver sometimes
feels insecure about the distance, depending on the state of the road surface on which
the own vehicle is traveling. However, if the own vehicle is controlled to take a
distance at which the driver never feels insecure in any road surface condition, the
driver can feel that such a distance is too long, and get annoyed.
[0007] It is therefore an object of the present invention to provide a vehicle control device
capable of setting, in any of various road surface conditions, an adequate distance
between an own vehicle and a preceding vehicle to suppress a feeling of insecurity
to be given to a driver.
[Solution to Technical Problem]
[0008] In order to achieve the above object, the present invention provides a vehicle control
device for controlling vehicle traveling. The vehicle control device comprises: a
surrounding vehicle detection part configured to detect a surrounding vehicle traveling
around an own vehicle; a road surface condition estimation part configured to estimate
a road surface condition which exerts an influence on a braking distance by a brake
of the own vehicle; a speed distribution setting part configured to set a speed limit
distribution defining a permissible upper limit relative speed, around the surrounding
vehicle detected by the surrounding vehicle detection part; and a control part configured
to control a speed and/or steering of the own vehicle to satisfy the speed limit distribution
set by the speed distribution setting part, wherein the speed distribution setting
part is configured to, when it is estimated by the road surface condition estimation
part that the road surface condition causes an increase in the braking distance, lower
the permissible upper limit relative speed.
[0009] In the vehicle control device of the present invention having the above feature,
the surrounding vehicle detection part operates to detect a surrounding vehicle traveling
around an own vehicle, and the road surface condition estimation part operates to
estimate a road surface condition which exerts an influence on a braking distance
by a brake of the own vehicle. The speed distribution setting part operates to set
a speed limit distribution defining a permissible upper limit relative speed, around
the surrounding vehicle detected by the surrounding vehicle detection part. Further,
the speed distribution setting part operates to, when it is estimated by the road
surface condition estimation part that the road surface condition causes an increase
in the braking distance, lower the permissible upper limit relative speed, and the
control part operates to control a speed and/or steering of the own vehicle to satisfy
this speed limit distribution.
[0010] According to this feature, when the road surface condition is estimated to cause
an increase in the braking distance, the permissible upper limit relative speed is
lowered, so that it is possible to increase a permissible inter-vehicle distance with
respect to the same relative speed, thereby suppressing a feeling of insecurity to
be given to a driver.
[0011] Preferably, in the vehicle control device of the present invention, the road surface
condition estimation part is configured to receive, from the surrounding vehicle detected
by the surrounding vehicle detection part, information regarding a traveling state
of the surrounding vehicle, and, using the received information, estimate whether
or not the road surface condition causes an increase in the braking distance.
[0012] The state of a road surface on which the own vehicle is traveling is not always uniform.
That is, the value of the road surface µ of the traveling road surface varies along
with traveling of the own vehicle, and the braking distance can also vary. For this
reason, sufficient estimation of the braking distance is hard to be achieved simply
by taking into account, e.g., weather and ambient temperature, and needs to more accurately
figure out the road surface condition. As one example, in
JP 5035419B, there is described a road surface friction coefficient estimation method in which
the road surface µ of a traveling road surface is estimated based on a lateral force
generated by a tire, a slip angle, a tire characteristic curve at a certain value
of the road surface µ, etc. As above, a technique of estimating the road surface µ
of a road surface on which a vehicle is traveling, based on a traveling state of the
vehicle, has been known. According to the above feature, information regarding a traveling
state of the surrounding vehicle is received from the surrounding vehicle, and it
is estimated, using the received information, whether or not the road surface condition
causes an increase in the braking distance, so that it is possible to finely estimate
the road surface condition and adequately set the speed limit distribution. Further,
the road surface condition is estimated using the information regarding the traveling
state transmitted from the surrounding vehicle, so that it is possible to estimate
not only the state of a road surface on which the own vehicle is currently traveling,
but also the state of a forward road surface on which the own vehicle will subsequently
travel, thereby early coping with a situation where the forward road surface condition
changes.
[0013] Preferably, in the vehicle control device of the present invention, the road surface
condition estimation part is configured to estimate a road surface µ of a traveling
lane, and, when the estimated road surface µ is equal to or less than a given value,
estimate that the road surface condition causes an increase in the braking distance,
wherein the speed distribution setting part is configured to, when the road surface
condition is estimated to cause an increase in the braking distance, lower the permissible
upper limit relative speed in a traveling direction of the own vehicle.
[0014] According to this feature, the road surface condition estimation part operates to
estimate a road surface µ of a traveling lane, and determine, based on the estimated
road surface µ, whether or not the road surface condition causes an increase in the
braking distance, so that it is possible to estimate the braking distance by a simple
method. Further, when the road surface condition is estimated to cause an increase
in the braking distance, the permissible upper limit relative speed in a traveling
direction of the own vehicle is lowered, so that it is possible to ensure sufficient
safety even when the braking distance is increased.
[0015] Preferably, in the vehicle control device of the present invention, the speed distribution
setting part is configured to set the speed limit distribution such that the permissible
upper limit relative speed becomes higher as a distance from the surrounding vehicle
becomes longer, and, when it is estimated by the road surface condition estimation
part that the road surface condition causes an increase in the braking distance, lower
the permissible upper limit relative speed with respect to the distance from the surrounding
vehicle.
[0016] According to this feature, when the road surface condition is estimated to cause
an increase in the braking distance, the permissible upper limit relative speed is
lowered with respect to the distance from the surrounding vehicle, and thereby a traveling
directional distance between the surrounding vehicle and the own vehicle is increased
with respect to the same relative speed, so that it is possible to sufficiently give
a driver a feeling of security even in the road surface condition causing an increase
in the braking distance.
[Effect of Invention]
[0017] The vehicle control device of the present invention can set, in any of various states
of a road surface on which the own vehicle is traveling, an adequate distance between
a preceding vehicle and the own vehicle to suppress a feeling of insecurity to be
given to a driver.
BRIEF DESCRIPTION OF DRAWINGS
[0018]
FIG. 1 is a configuration diagram of a vehicle control device according to one embodiment
of the present invention.
FIG. 2 is a control block diagram of the vehicle control device according to this
embodiment.
FIG. 3 is an explanatory diagram of a first target traveling course to be set by the
vehicle control device according to this embodiment.
FIG. 4 is an explanatory diagram of a second target traveling course to be set by
the vehicle control device according to this embodiment.
FIG. 5 is an explanatory diagram of a third target traveling course to be set by the
vehicle control device according to this embodiment.
FIG. 6 is an explanatory diagram of obstacle avoidance based on correction of a target
traveling course in the vehicle control device according to this embodiment.
FIG. 7 is an explanatory diagram showing a relationship between a permissible upper
limit relative speed and a distance between a surrounding vehicle and an own vehicle
during avoidance of the surrounding vehicle, in the vehicle control device according
to this embodiment.
FIG. 8 is an explanatory diagram of a vehicle model in the vehicle control device
according to this embodiment.
FIG. 9 is a flowchart of a driving support control processing routine in the vehicle
control device according to this embodiment.
FIG. 10 is a flowchart of speed limit distribution setting processing in the vehicle
control device according to this embodiment.
FIG. 11 is an explanatory diagram of estimation of a road surface µ in the vehicle
control device according to this embodiment.
FIG. 12 is a graph showing a change in the permissible upper limit relative speed
under the condition that the road surface µ is relatively low, in the vehicle control
device according to this embodiment.
FIG. 13 is a diagram showing a change in speed limit distributions under the condition
that the road surface µ is relatively low, in the vehicle control device according
to this embodiment.
FIG. 14 is a graph showing a modification of setting of a correction coefficient under
the condition that the road surface µ is relatively low.
DESCRIPTION OF EMBODIMENTS
[0019] With reference to the accompanying drawings, a vehicle control device according to
one embodiments of the present invention will now be described. First of all, with
reference to FIGS. 1 and 2, the configuration of the vehicle control device will be
described. FIG. 1 is a configuration diagram of the vehicle control device, and FIG.
2 is a control block diagram of the vehicle control device.
[0020] The vehicle control device 100 according to this embodiment is configured to provide,
to a vehicle 1 (see FIG. 3, etc.) equipped with this device, various driving support
controls each based on a respective one of a plurality of driving support modes. From
among the plurality of driving support modes, a driver can select one desired driving
support mode.
[0021] As shown in FIG. 1, the vehicle control device 100 comprises: a vehicle control and
computing unit (ECU) 10, a plurality of sensors and switches, a plurality of control
systems, and a driver manipulation unit (not shown) for allowing user input regarding
the driving support modes, each equipped in the vehicle (own vehicle) 1. The sensors
and switches include: a camera 21 for capturing an image of a vehicle exterior of
the vehicle; a millimeter-wave radar 22; a vehicle speed sensor 23 for detecting the
behavior of the vehicle; a position measurement system 24; a navigation system 25;
and an inter-vehicle communication system 26. Further, the control systems include
an engine control system 31, a brake control system 32 and a steering control system
33.
[0022] The ECU 10 illustrated in FIG. 1 is composed of a computer comprising a CPU, a memory
storing therein various programs, and an input-output device. The ECU 10 is configured
to be operable, based on a driving support mode selection signal and a setting vehicle
speed signal received from the driver manipulation unit, and signals received from
the sensors and switches, to output request signals for appropriately operating an
engine system, a brake system and a steering system, respectively, to the engine control
system 31, the brake control system 32 and the steering control system 33.
[0023] The camera 21 is configured to capture an image forward of the vehicle 1 and output
captured image data. The ECU 10 is operable to identify an object (e.g., a vehicle,
a pedestrian, a road, a demarcation line (a lane border line, a white road line or
a yellow road line), a traffic light, a traffic sign, a stop line, an intersection,
an obstacle or the like) based on the image data. Additionally, it is possible to
provide a vehicle exterior camera for capturing an image laterally outward or rearward
of the vehicle 1. The vehicle may also be equipped with a vehicle interior camera
for capturing an image of the driver during driving of the vehicle.
[0024] The millimeter-wave radar 22 is a measurement device for measuring the position and
speed of the object (particularly, a preceding vehicle, a parked vehicle, a pedestrian,
an obstacle or the like), and is configured to transmit a radio wave (transmitted
wave) forwardly with respect to the vehicle 1 and receive a reflected wave produced
as a result of reflection of the transmitted wave by the object. The millimeter-wave
radar 22 is further configured to measure, based on the transmitted wave and the received
wave, a distance between the vehicle 1 and the object, i.e., a vehicle-object distance,
(e.g., inter-vehicle distance) and/or a relative speed of the object with respect
to the vehicle 1. In this embodiment, as the millimeter-wave radar 22, there are provided
a forward radar for detecting an object forward of the vehicle 1, a lateral radar
for detecting an object laterally outward of the vehicle 1; and a rearward radar for
detecting an object rearward of the vehicle 1. Here, a laser radar, an ultrasonic
sensor or the like may be used, as a substitute for the millimeter-wave radar 22,
to measure the distance and/or the relative speed with respect to the object. Further,
the position and speed measurement device may be composed using a plurality of other
sensors.
[0025] The vehicle speed sensor 23 is configured to detect an absolute speed of the vehicle
1.
[0026] The position measurement system 24 is composed of a GPS system and/or a gyro system,
and is configured to detect the position of the vehicle 1 (current vehicle position
information).
[0027] The navigation system 25 stores therein map information, and is configured to be
operable to provide the map information to the ECU 10. Then, the ECU 10 is operable,
based on the map information and the current vehicle position information, to identify
a road, an intersection, a traffic light, a building and others existing around the
vehicle 1 (particularly, forward of the vehicle 1 in its travelling direction). It
is to be understood that the map information may be stored in the ECU 10.
[0028] The inter-vehicle communication system 26 is a vehicle-to-vehicle communication
system, and is configured to exchange information about vehicle position, information
about traveling speed, information about driver's manipulation for acceleration/deceleration,
steering or the like, between the own vehicle and a surrounding vehicle traveling
around the own vehicle. Through the use of the inter-vehicle communication system
26, it is possible to acquire information about the position, speed, driver's manipulation
such as steering wheel turning angle, vehicle attitude angle and others of a vehicle
parked or traveling on a traveling course of the own vehicle with a relatively long
distance therebetween.
[0029] The engine control system 31 comprises a controller for controlling an engine of
the vehicle 1. The ECU 10 is operable, when there is a need to accelerate or decelerate
the vehicle 1, to output, to the engine control system 31, an engine output change
request signal for requesting to change an engine output so as to obtain a target
acceleration/deceleration.
[0030] The brake control system 32 comprises a controller for controlling a braking device
of the vehicle 1. The ECU 10 is operable, when there is a need to decelerate the vehicle
1, to output, to the brake control system 32, a braking request signal for requesting
to generate a braking force to be applied to the vehicle 1, so as to obtain the target
acceleration/deceleration.
[0031] The steering control system 33 comprises a controller for controlling a steering
device of the vehicle 1. The ECU 10 is operable, when there is a need to change the
travelling direction of the vehicle 1, to output, to the steering control system 33,
a steering direction change request signal for requesting to change a steering direction
so as to obtain a target steering angle.
[0032] As shown in FIG. 2, the ECU 10 comprises a single CPU functioning as an input processing
part 10a, a surrounding vehicle detection part 10b, a target traveling course calculation
part 10c, a road surface condition estimation part 10d, a speed distribution setting
part 10e, and a control part 10f. In this embodiment, the ECU 10 is configured such
that the above functions are executed by the single CPU. Alternatively, the ECU may
be configured such that the above functions are executed by a plurality of CPUs.
[0033] The input processing part 10a is configured to process input information from the
vehicle exterior camera 20, other sensors and the driver manipulation unit 35. Specifically,
the input processing part 10a functions as an image analysis part for analyzing an
image of a traveling road captured by the camera 21 to detect a traveling lane in
which the own vehicle is traveling (demarcation lines on opposed lateral sides of
the lane).
[0034] The surrounding vehicle detection part 10b is configured to detect a surrounding
vehicle traveling around the own vehicle, etc., based on input information from the
millimeter-wave radar 22, the camera 21, the inter-vehicle communication system 26
and others.
[0035] The target traveling course calculation part 10c is configured to calculate a target
traveling course of the own vehicle, based on input information from the millimeter-wave
radar 22, the camera 21, the sensors and others.
[0036] The road surface condition estimation part 10d is configured to estimate a road surface
condition which exerts an influence on a braking distance by a brake of the own vehicle
1, based on input information from the millimeter-wave radar 22, the camera 21, the
navigation system 25, the inter-vehicle communication system 26 and others. The estimation
of the road surface condition by the road surface condition estimation part 10d will
be described later.
[0037] The speed distribution setting part 10e is configured to set, around a surrounding
vehicle, a speed limit distribution defining a permissible upper limit relative speed.
For example, the speed distribution setting part 10e is operable, when a surrounding
vehicle to be avoided is detected by the surrounding vehicle detection part 10b, to
set a distribution line of a permissible upper limit relative speed at which the own
vehicle 1 is permitted to travel with respect to the surrounding vehicle (speed limit
distribution). Further, when an object other than a vehicle to be avoided is detected
by the surrounding vehicle detection part 10b, the speed distribution setting part
10e is also operable to set a speed limit distribution around the detected object.
[0038] The control part 10f is configured to control the speed and steering of the own vehicle
to satisfy the speed limit distribution which is a distribution line of a permissible
upper limit relative speed at which the own vehicle is permitted to travel with respect
to the surrounding vehicle. Specifically, the control part 10f is operable to correct
the target traveling course calculated by the target traveling course calculation
part 10c, to satisfy the speed limit distribution, thereby calculating a plurality
of corrected traveling course candidates. Then, the control part 10f is operable to
select, from among the corrected traveling course candidates satisfying the speed
limit distribution, one or more corrected traveling course candidates satisfying a
given limiting condition. Then, the control part 10f is operable, from among the selected
one or more corrected traveling course candidates, to set, as an optimal corrected
traveling course, a corrected traveling course candidate which is the smallest in
terms of a given evaluation function. That is, the control part 10f is configured
to calculate the corrected traveling course, based on the speed limit distribution,
the given evaluation function and the given limiting condition. Here, in this embodiment,
the limiting condition for determining an optimal corrected traveling course is appropriately
set based on a currently selected one of the driving support modes, and a state of
driving by a driver. It should be noted that the control part 10f may be configured
to generate a traveling course satisfying the speed limit distribution, without using
the limiting condition and the evaluation function.
[0039] Then, the control part 10f is operable to generate a request signal for allowing
the own vehicle to travel along the determined optimal corrected traveling course,
and output the generated request signal to one or more of at least the engine control
system 31, the brake control system 32 and the steering control system 33.
[0040] Next, the driving support modes to be executed by the vehicle control device 100
according to this embodiment will be described. In this embodiment, the driving support
modes consist of four modes. Specifically, the driving support modes consist of: a
speed limiting mode which is a manual steering mode; a preceding vehicle following
mode which is an automatic steering mode; an automatic speed control mode which is
a manual steering mode; and a basic control mode which is to be executed when none
of the above three driving support modes is selected.
< Preceding Vehicle Following Mode >
[0041] The preceding vehicle following mode is basically an automatic steering mode in which
the vehicle 1 is controlled to travel following a preceding vehicle, while maintaining
a given inter-vehicle distance between the vehicle 1 and the preceding vehicle, and
involves steering control, speed control (engine control and/or brake control), and
obstacle avoidance control (the speed control and the steering control) to be automatically
executed by the vehicle control device 100.
[0042] In the preceding vehicle following mode, each of the steering control and the speed
control is performed in different manners depending on detectability of opposed lane
edges, and the presence or absence of a preceding vehicle. Here, the term "opposed
lane edges" means opposed edges (one of which is a demarcation line such as a white
road line, a road edge, an edge stone, a median strip, a guardrail or the like) of
a lane in which the vehicle 1 is traveling, i.e., borderlines with respect to, e.g.,
a neighboring lane and sidewalk. The input processing part 10a comprised in the ECU
10 is operable to detect the opposed lane edges from the image data captured by the
camera 21. Alternatively, the input processing part 10a may be configured to detect
the opposed lane edges from the map information of the navigation system 25. However,
for example, in a situation where the vehicle 1 is traveling on the plain on which
there is no traffic lane, instead of on a well-maintained road, or in a situation
where reading of the image data from the camera 21 is bad, there is a possibility
of failing to detect the opposed lane edges.
[0043] Further, in this embodiment, the ECU 10 is operable, when serving as a preceding
vehicle detection part, to detect a preceding vehicle, based on the image data from
the camera 21, and the measurement data from the forward radar comprised in the millimeter-wave
radar 22. Specifically, the ECU 10 is operable to detect, as a preceding vehicle,
a second vehicle which is traveling forward of the vehicle 1, based on the image data
from the camera 21. Further, in this embodiment, the ECU 10 is operable, when the
inter-vehicle distance between the vehicle 1 and the second vehicle is determined
to be equal to or less than a given value (e.g., 400 to 500 m), based on the measurement
data from the millimeter-wave radar 22, to detect the second vehicle as a preceding
vehicle.
[0044] In a situation where, in the preceding vehicle following mode, a surrounding object
to be avoided is detected by the input processing part 10a, the target traveling course
is corrected to automatically avoid the obstacle (surrounding object), irrespective
of the presence or absence of a preceding vehicle, and the detectability of opposed
lane edges.
< Automatic Speed Control Mode >
[0045] The automatic speed control mode is a manual steering mode in which the speed control
is performed such that the vehicle 1 maintains a given setup vehicle speed (constant
speed) preliminarily set by the driver, and which involves the speed control (the
engine control and/or the brake control) to be automatically executed by the vehicle
control device 100, but does not involves the steering control. In this automatic
speed control mode, although the vehicle 1 is controlled to travel while maintaining
the setup vehicle speed, the driver can increase the vehicle speed beyond the setup
vehicle speed by depressing an accelerator pedal. Further, when the driver performs
brake manipulation, priority is given to the intent of the driver, and therefore the
vehicle 1 is decelerated from the setup vehicle speed. Further, when the vehicle 1
catches up to a preceding vehicle, the speed control is performed such that the vehicle
1 follows the preceding vehicle while maintaining an inter-vehicle distance appropriate
to a follow-up vehicle speed, and then when the preceding vehicle disappears, the
speed control is performed such that the follow-up vehicle speed is returned to the
setup vehicle speed.
< Speed Limiting Mode >
[0046] The speed limiting mode is a manual steering mode in which the speed control is performed
to prevent the vehicle speed of the vehicle 1 from exceeding a speed limit (legal
speed limit) designated by a speed sign, or the setup vehicle speed set by the driver,
and which involves the speed control (engine control) to be automatically executed
by the vehicle control device 100. With regard to the speed limit, the ECU 10 may
be configured to subject image data about an image of a speed sign or a speed marking
on a road surface captured by the camera 21, to image recognition processing, to identify
the legal speed limit, or may be configured to receive information regarding the speed
limit from the outside via a wireless communication. In the speed limiting mode, even
when the driver depresses the accelerator pedal so as to increase the vehicle speed
beyond the speed limit or the setup vehicle speed, the vehicle speed of the vehicle
1 is increased only up to the speed limit or the setup vehicle speed.
< Basic Control Mode >
[0047] The basic control mode is a mode (off mode) in which none of the above three driving
support modes is selected, and the steering control and speed control are not automatically
executed by the vehicle control device 100. However, in a situation where there is
a possibility that the vehicle 1 collides with a surrounding vehicle such as an oncoming
vehicle or the like, collision avoidance control is executed. It should be noted that
this avoidance control is executed in the preceding vehicle following mode, the automatic
speed control mode and the speed limiting mode, in the same manner.
[0048] Next, with reference to FIGS. 3 to 5, a plural of traveling courses to be computed
by the vehicle control device 100 according to this embodiment will be described.
FIGS. 3 to 5 are explanatory diagrams of first to third traveling courses, respectively.
In this embodiment, the target traveling course calculation part 10c comprised in
the ECU 10 is configured to compute the first to third traveling courses R1 to R3
temporally repeatedly (e.g., at intervals of 0.1 sec). In this embodiment, the ECU
10 is operable, based on information from the sensors and others, to compute a traveling
course in a time period from the present time through until a given time period (e.g.,
3 sec) elapses. The traveling course Rx (where x = 1, 2, 3) is defined by a target
position (Px_k) and a target speed (Vx_k) (where k = 0, 1, 2, - - -, n) of the vehicle
1 on the traveling course. Further, at each of the target positions, target values
of a plurality of variables (acceleration, acceleration change rate, yaw rate, steering
angle, vehicle angle, etc.) are specified in addition to the target speed.
[0049] Each of the traveling courses (first to third traveling courses) in FIGS. 3 to 5
is computed based on the shape of a traveling road on which the vehicle 1 is traveling,
a traveling trajectory of a preceding vehicle, the traveling behavior of the vehicle
1, and the setup vehicle speed, without taking into account surrounding object detection
information regarding an object (an obstacle such as a surrounding vehicle or a pedestrian)
on the traveling road or around the traveling road. Thus, in this embodiment, each
of the traveling courses is computed without taking into account information about
surrounding objects, so that it is possible to keep down the overall computational
load of these traveling courses.
[0050] For the sake of facilitating understanding, the following description will be made
based on an example in which each of the traveling courses is computed on the assumption
that the vehicle 1 travels on a road 5 consisting of a straight section 5a, a curve
section 5b, a straight section 5c. The road 5 comprises left and right lanes 5L, 5R.
Assume that, at the present time, the vehicle 1 travels on the lane 5L in the straight
section 5a.
(First Traveling Course)
[0051] As shown in FIG. 3, the first traveling course R1 is set, by a distance corresponding
to a given time period, to allow the vehicle 1 to maintain traveling in the lane 5L
serving as the traveling road, in conformity to the shape of the road 5. Specifically,
the first traveling course R1 is set, in each of the straight sections 5a, 5c, to
allow the vehicle 1 to maintain traveling along approximately the widthwise middle
of the lane 5L, and set, in the curve section 5b, to allow the vehicle 1 to travel
on an inner side or in-side (on the side of a center O of a curvature radius L of
the curve section 5b) with respect to the widthwise middle of the lane 5L.
[0052] The target traveling course calculation part 10c is operable to execute the image
recognition processing for image data about the surroundings of the vehicle 1, captured
by the camera 21, to detect opposed lane edges 6L, 6R. The opposed lane edges are,
e.g., a demarcation line (white road line or the like), and a road shoulder, as mentioned
above. Further, the target traveling course calculation part 10c is operable, based
on the detected opposed lane edges 6L, 6R, to calculate a lane width W of the lane
5L and the curvature radius L in the curve section 5b. Alternatively, the target traveling
course calculation part 10c may be configured to acquire the lane width W and the
curvature radius L from the map information of the navigation system 25. Further,
the target traveling course calculation part 10c is operable to read, from the image
data, a speed limit indicated by a speed sign S or on the road surface. Alternatively,
the target traveling course calculation part 10c may be configured to acquire the
speed limit from the outside via a wireless communication, as mentioned above.
[0053] With regard to the straight sections 5a, 5c, the target traveling course calculation
part 10c is operable to set a plurality of target positions P1_k of the first traveling
course R1 to allow a vehicle width directional center (e.g., the position of the center
of gravity) of the vehicle 1 to pass through the widthwise middle between the opposed
lane edges 6L, 6R.
[0054] On the other hand, with regard to the curve section 5b, the target traveling course
calculation part 10c is operable to maximally set a displacement amount Ws toward
the in-side from the widthwise middle position of the lane 5L at a longitudinal middle
position P1_c of the curve section 5b. This displacement amount Ws is computed based
on the curvature radius L, the lane width W, and a width dimension D of the vehicle
1 (prescribed values stored in the memory of the ECU 10). Then, the target traveling
course calculation part 10c is operable to set the plurality of target positions P1_k
of the first traveling course R1 in such a manner as to smoothly connect the longitudinal
middle position P1_c of the curve section 5b to the widthwise middle position of each
of the straight sections 5a, 5b. Here, it should be understood that the first traveling
course R1 may also be offset toward the in-side in the straight sections 5a, 5c at
positions just before entering the curve section 5b and just after exiting the curve
section 5b.
[0055] Basically, a target speed V1_k at each of the target positions P1_k of the first
traveling course R1 is set to a given setup vehicle speed (constant speed) set by
the driver or preliminarily set by the vehicle control device 100. However, when this
setup vehicle speed exceeds a speed limit acquired from a speed sign S or the like,
or a speed limit determined according to the curvature radius L of the curve section
5b, the target speed V1_k at each of the target positions P1_k on the traveling course
is limited to a lower one of the two speed limits. Further, the target traveling course
calculation part 10c is operable to appropriately correct the target positions P1_k
and the target speed V1_k, according to a current behavior state (i.e., vehicle speed,
acceleration, yaw rate, steering angle, lateral acceleration, etc.) of the vehicle
1. For example, when a current value of the vehicle speed is largely different from
the setup vehicle speed, the target speed is corrected so as to allow the vehicle
speed to come close to the setup vehicle speed.
(Second Traveling Course)
[0056] As shown in FIG. 4, the second traveling course R2 is set, by a distance corresponding
to a given time period, to allow the vehicle 1 to follow a traveling trajectory of
a preceding vehicle 3. The target traveling course calculation part 10c is operable
to continuously compute the position and speed of the preceding vehicle 3 in the lane
5L in which the vehicle 1 is traveling, based on the image data from the camera 21,
the measurement data from the millimeter-wave radar 22, and the vehicle speed of the
vehicle 1 from the vehicle speed sensor 23, and store the calculated position and
speed as preceding vehicle trajectory information, and, based on the preceding vehicle
trajectory information, to set the traveling trajectory of the preceding vehicle 3
as the second traveling course R2 (target positions P2_k and target speeds V2_k).
(Third Traveling Course)
[0057] As shown in FIG. 5, the third traveling course R3 is set, by a distance corresponding
to a given time period, based on a current driving state of the vehicle 1 by the driver.
Specifically, the third traveling course R3 is set based on a position and a speed
estimated from a current traveling behavior of the vehicle 1.
[0058] The target traveling course calculation part 10c is operable, based on the steering
angle, the yaw rate and the lateral acceleration of the vehicle 1, to compute target
positions P3_k of the third traveling course R3 having the distance corresponding
to the given time period. However, in the situation where the opposed lane edges are
detected, the target traveling course calculation part 10c is operable to correct
the target positions P3_k such that the computed third traveling course R3 does not
come close to or intersect with any of the lane edges.
[0059] Further, the target traveling course calculation part 10c is operable, based on current
values of the vehicle speed and the acceleration of the vehicle 1, to compute a target
speed V3_k of the third traveling course R3 having the distance corresponding to the
given time period. Here, when the target speed V3_k exceeds the speed limit acquired
from the speed sign S or the like, the target speed V3_k may be corrected in such
a manner as to avoid exceeding the speed limit.
[0060] Next, a relationship between the driving support modes and the target traveling
courses in the vehicle control device 100 will be described. In this embodiment, the
vehicle control device 100 is configured such that, when the driver selects one of
the driving support modes, one of the traveling courses is selected, as the target
traveling course, according to the selected driving support mode.
[0061] When the preceding vehicle following mode is selected in a situation where opposed
lane edges are detected, the first traveling course is used as the target traveling
course, irrespective of the presence or absence of a preceding vehicle. In this case,
the setup vehicle speed is used as the target speed.
[0062] On the other hand, when the preceding vehicle following mode is selected in a situation
where no opposed lane edges are detected, but a preceding vehicle is detected, the
second traveling course is used as the target traveling course. In this case, the
target speed is set according to the vehicle speed of the preceding vehicle. Further,
when the preceding vehicle following mode is selected in a situation where neither
opposed lane edges nor a preceding vehicle is detected, the third traveling course
is used as the target traveling course.
[0063] When the automatic speed control mode is selected, the third traveling course is
used as the target traveling course. In the automatic speed control mode in which
the speed control is automatically executed as mentioned above, the setup speed is
used as the target speed. Further, the driver manually controls steering by manipulating
a steering wheel.
[0064] When the speed limiting mode is selected, the third traveling course is also used
as the target traveling course. In the speed limiting mode in which the speed control
is automatically executed as mentioned above, the target speed is set according to
a depression amount of the accelerator pedal manipulated by the driver, within the
speed limit. Further, the driver manually controls steering by manipulating the steering
wheel.
[0065] When the basic control mode (off mode) is selected, the third traveling course is
used as the target traveling course. The basic control mode is basically the same
as the speed limiting mode in a state in which no speed limit is set.
[0066] Next, with respect to FIGS. 6 to 8, traveling course correction processing to be
executed by the control part 10f of the ECU in the vehicle control device 100 according
to this embodiment will be described. FIG. 6 is an explanatory diagram of obstacle
avoidance by correction of the target traveling course. FIG. 7 is an explanatory diagram
showing a relationship between the permissible upper limit relative speed and a distance
between a surrounding vehicle and an own vehicle during avoidance of the surrounding
vehicle. FIG. 8 is an explanatory diagram of a vehicle model.
[0067] In FIG. 6, the vehicle 1 is traveling on a traveling road (lane) 7, and is just about
passing by a traveling or parked vehicle 3 (surrounding vehicle) and overtaking the
vehicle 3.
[0068] Generally, when passing by (or overtaking) an obstacle (e.g., a preceding vehicle,
a parked vehicle, or a pedestrian) on or near a road, a driver of the vehicle 1 keeps
a given clearance or distance (lateral distance) between the vehicle 1 and the obstacle
in a lateral direction orthogonal to the traveling direction of the vehicle 1, and
reduces the vehicle speed to a value the driver of the vehicle 1 feels safe. Specifically,
in order to avoid dangers such as a situation where a preceding vehicle suddenly changes
a course, a situation where a pedestrian comes out from a blind spot due to the obstacle,
and a situation where a door of a parked vehicle is suddenly opened, the relative
speed with respect to the obstacle is set to a lower value as the clearance becomes
smaller.
[0069] Further, generally, when the vehicle 1 is approaching a preceding vehicle from behind
the preceding vehicle, the driver of the vehicle 1 adjusts the vehicle speed (relative
speed) according to the inter-vehicle distance (longitudinal distance) along the travelling
direction. Specifically, when the inter-vehicle distance is relatively large, an approaching
speed (relative speed) is maintained relatively high. However, when the inter-vehicle
distance becomes relatively small, the approaching speed is set to a lower value.
Subsequently, at a given inter-vehicle distance, the relative speed between the two
vehicles is set to zero. This action is the same even when the preceding vehicle is
a parked vehicle.
[0070] As above, the driver drives the vehicle 1 in such a manner as to avoid dangers while
taking into account a relationship between the distance (including the lateral distance
and the longitudinal distance) from the vehicle 1 to an obstacle, and the relative
speed therebetween.
[0071] Therefore, in this embodiment, as shown in FIG. 6, the vehicle 1 is configured to
set a two-dimensional distribution (speed limit distribution 40) defining the permissible
upper limit relative speed in the travelling direction of the vehicle 1 with respect
to an obstacle (such as the parked vehicle 3) detected by the vehicle 1, around the
obstacle (over laterally-outward, rearward and forward regions around the obstacle)
or at least between the obstacle and the vehicle 1. In the speed distribution 40,
the permissible upper limit relative speed V
lim is set at each point around the obstacle. In this regard, the speed distribution
setting part 10e is operable to set a plurality of speed limit distributions 40 according
to a distance from the surrounding vehicle 3. In this embodiment, in all the driving
support modes, traveling course correction processing is executed to prevent the relative
speed of the vehicle 1 with respect to the obstacle from exceeding the permissible
upper limit relative speed V
lim in each of the speed limit distributions 40. Further, as mentioned in detail later,
when the obstacle is a surrounding vehicle, the speed limit distributions 40 are set
around the obstacle differently depending on information received from the surrounding
vehicle via the inter-vehicle communication system 26, etc.
[0072] As can be understood from FIG. 6, in the speed limit distributions 40, the permissible
upper limit relative speed is set such that it becomes smaller as the lateral distance
and the longitudinal distance from the obstacle become smaller (as the vehicle 1 approaches
the obstacle more closely). Specifically, the speed limit distributions 40 are set
as a plurality of (in this example, four) constant relative speed lines each connecting
the same upper limits. The constant relative speed lines a, b, c, d represent, respectively,
to the speed limit distributions 40 in which the permissible upper limit relative
speed V
lim is 0 km/h, 20 km/h, 40 km/h and 60 km/h. In this example, each of the speed limit
distributions 40 is set to have an approximately rectangular shape. In this regard,
the speed distribution setting part 10e is operable, when an obstacle (surrounding
object) to be avoided is recognized by the input processing part 10a, to set the speed
limit distributions 40 each of which is a distribution line of a permissible upper
limit relative speed at which the own vehicle is permitted to travel with respect
to the obstacle. Then, the control part 10f is operable to correct the target traveling
course calculated by the target traveling course calculation part 10c, in such a manner
as to satisfy the speed limit distributions 40.
[0073] Here, the speed limit distributions 40 do not necessarily have to be set over the
entire circumference of the obstacle, but may be set at least in a region rearward
of the obstacle and on one (in FIG. 6, right side) of opposite lateral sides of the
obstacle on which the vehicle 1 exists. Further, the speed limit distributions 40
may be set to have a unsymmetrical shape.
[0074] As shown in FIG. 7, when the vehicle 1 travels at a certain relative speed with respect
to an obstacle (in the example illustrated in FIG. 6, the vehicle 3 as the obstacle
is parked, and therefore the relative speed is equal to the absolute speed of the
vehicle 1), the permissible upper limit relative speed V
lim is set such that it quadratically increases with respect to a distance from the obstacle.
That is, with respect to a lateral clearance X from the obstacle, the permissible
upper limit relative speed V
lim is set by the following formula (1):
[0075] In the formula (1), k
1 denotes a gain coefficient related to the degree of change of V
lim with respect to the lateral clearance X, and is set depending on the type of obstacle
and the like. A safe distance D
X0 can also be set depending on the type of obstacle and the like. As one example, in
this embodiment, the safe distance D
X0 is set to 0.2 [m]. Further, a correction coefficient α is a coefficient to be used
when the obstacle is a surrounding vehicle, wherein it is changed according to information
regarding manipulation by a driver of the surrounding vehicle, etc., received from
the surrounding vehicle via the inter-vehicle communication system 26. Setting of
the correction coefficient α will be described later.
[0076] Further, as shown in the formula (1), in the lateral direction of the obstacle, the
permissible upper limit relative speed V
lim is kept at 0 (zero) km/h until the lateral clearance X reaches the safe distance
D
X0, and quadratically increases when the lateral clearance X becomes equal to or greater
than the safe distance D
X0. That is, in order to ensure safety, when the lateral clearance X is less than the
safe distance D
X0, the relative speed to be permitted for the vehicle 1 is set to zero. On the other
hand, when the lateral clearance X is equal to or greater than the safe distance D
X0, the vehicle 1 is permitted to pass by the obstacle at a relatively large relative
speed.
[0077] Further, in the longitudinal direction of the obstacle (the travelling direction
of the vehicle 1), the permissible upper limit relative speed V
lim [km/h] is set, with respect to a traveling directional distance Y to the obstacle,
by the following formula (2):
[0078] In the formula (2), Vs [km/h] denotes a traveling speed of the own vehicle 1, and
k
2 denotes a gain coefficient related to the degree of change of V
lim with respect to the traveling directional distance Y (distance to the obstacle),
and is set depending on the type of obstacle and the like. A safe distance D
Y0 can also be set depending on the type of obstacle and the like. As one example, in
this embodiment, the safe distance D
Y0 is set to 2 [m]. Further, correction coefficient β is coefficient to be used when
the obstacle is a surrounding vehicle, wherein it is changed according to information
regarding manipulation by a driver of the surrounding vehicle, etc., received from
the surrounding vehicle via the inter-vehicle communication system 26 and the like.
Setting of the correction coefficients β will be described later.
[0079] As expressed in the formula (2), in the traveling direction (longitudinal direction)
of the own vehicle, the permissible upper limit relative speed V
lim is kept at 0 (zero) km/h until the longitudinal distance Y reaches the safe distance
D
Y0, and quadratically increases when the longitudinal distance Y becomes equal to or
greater than the safe distance D
Y0. That is, in order to ensure safety, when the longitudinal distance Y to the obstacle
is less than the safe distance D
Y0, the relative speed to be permitted for the vehicle 1 is set to zero. On the other
hand, when the longitudinal distance Y is equal to or greater than the safe distance
D
Y0, the vehicle 1 is permitted to approach the obstacle at a relatively large relative
speed. Further, in the longitudinal direction, the permissible upper limit relative
speed V
lim is set to be inversely proportional to the traveling speed Vs of the own vehicle
1. That is, considering that a braking distance of the own vehicle 1 becomes longer
as the traveling speed Vs of the own vehicle 1 becomes higher, the permissible upper
limit relative speed V
lim is set to become lower as the traveling speed Vs of the own vehicle 1 becomes higher.
Thus, the permissible upper limit relative speed V
lim for the same longitudinal distance Y becomes lower as the traveling speed Vs of the
own vehicle 1 becomes higher.
[0080] In this embodiment, V
lim in each id the lateral and longitudinal directions is defined as a quadratic function.
Alternatively, V
lim may be defined as another function (e.g., a linear function). Further, the permissible
upper limit relative speed V
lim in the lateral direction of the obstacle and the permissible upper limit relative
speed V
lim in a region rearward of the obstacle have been described with reference to FIG. 7.
However, the permissible upper limit relative speed V
lim may be set in every radial directions including a longitudinal direction in a region
forward of the obstacle. In this case, the coefficient k and the safe distance Do
may be set depending on a direction from the obstacle.
[0081] The speed limit distributions 40 can be set based on various parameters. Examples
of the parameter may include the relative speed between the vehicle 1 and the obstacle,
the type of the obstacle, the traveling direction of the vehicle 1, a moving direction
and a moving speed of the obstacle, the length of the obstacle, and the absolute speed
of the vehicle 1. That is, based on these parameters, the coefficient k and the safe
distance Do can be selected.
[0082] In this embodiment, the obstacle includes a vehicle, a pedestrian, a bicycle, a cliff,
a trench, a hole and a fallen object. The vehicle can be classified into a passenger
vehicle, a truck, and a motorcycle. The pedestrian can be classified into an adult,
a child and a group.
[0083] As shown in FIG. 6, when the vehicle 1 is traveling on the traveling road 7, the
input processing part 10a comprised in the ECU 10 of the vehicle 1 operates to detect
an obstacle (vehicle 3) based on the image data from the camera 21. At this moment,
the type of the obstacle (in this example, a vehicle or a pedestrian) is identified.
[0084] Further, the input processing part 10a operates to calculate the position and the
relative speed of the obstacle (vehicle 3) with respect to the vehicle 1, and the
absolute speed of the obstacle, based on the measurement data from the millimeter-wave
radar 22 and vehicle speed data from the vehicle speed sensor 23. Here, the position
of the obstacle includes a y-directional position (longitudinal distance) along the
traveling direction of the vehicle 1, and an x-directional position (lateral distance)
along the lateral direction orthogonal to the traveling direction.
[0085] The speed distribution setting part 10e comprised in the ECU 10 operates to set
the speed limit distributions 40 with respect to each of one or more detected obstacles
(in FIG. 6, the vehicle 3). Then, the control part 10f operates to correct a traveling
course to prevent the speed of the vehicle 1 from exceeding the upper limits V
lim in the speed limit distributions 40. That is, along with avoidance of the obstacle,
the control part 10f operates to correct the target traveling course determined according
to the driving support mode selected by the driver.
[0086] Specifically, in a situation where, if the vehicle 1 travels along the target traveling
course, the target speed exceeds, at a certain target position, the permissible upper
limit relative speed defined in one of the speed distributions 40, the target speed
is reduced without changing the target positions (course Rc1 in FIG. 6), or the target
positions are changed to points on a bypass course so as to allow the target speed
to avoid exceeding the permissible upper limit relative speed (course Rc3 in FIG.
6) or both the target positions and the target speed are changed (course Rc2 in FIG.
6).
[0087] For example, FIG. 6 shows a case where the computed target traveling course R is
a course which is set such that the vehicle 1 travels along the widthwise middle of
the traveling road 7 (target positions) at 60 km/h (target speed). In this case, the
parked vehicle 3 as the obstacle exists forward of the vehicle 1. However, in the
stage of computing the target traveling course R, this obstacle is not taken into
account to reduce the computational load, as mentioned above.
[0088] If the vehicle 1 travels along the target traveling course R, it will cut across
the constant relative speed lines d, c, c, d of the speed limit distributions 40,
in this order. That is, the vehicle 1 traveling at 60 km/h enters a region inside
the constant relative speed line d (permissible upper limit relative speed V
lim = 60 km/h). Thus, the control part 10f operates to correct the target traveling course
R so as to limit the target speed at each target position of the target traveling
course R to the permissible upper limit relative speed V
lim or less, thereby generating the post-correction target traveling course (corrected
traveling course candidate) Rc1. Specifically, in the post-correction target traveling
course Rc1, as the vehicle 1 approaches the vehicle 3, the target speed is reduced
to become equal to or less than the permissible upper limit relative speed V
lim at each target position, i.e., gradually reduced to less than 40 km/h, and then,
as the vehicle 1 travels away from the vehicle 3, the target speed is gradually increased
to 60 km/h as the original vehicle speed.
[0089] The post-correction target traveling course (corrected traveling course candidate)
Rc3 is a course which is set such that the vehicle 1 travels outside the constant
relative speed line d (which corresponds to a relative speed of 60 km/h), instead
of changing the target speed (60 km/h) of the target traveling course R. In this case,
the control part 10f operates to correct the target traveling course R such that the
target positions are changed to points on or outside the constant relative speed line
d, while maintain the target speed of the target traveling course R, thereby generating
the post-correction target traveling course Rc3. Thus, the target speed of the post-correction
target traveling course Rc3 is maintained at 60 km/h as the target speed of the target
traveling course R.
[0090] The post-correction target traveling course (corrected traveling course candidate)
Rc2 is a course set by changing both the target positions and the target speed of
the target traveling course R. In the post-correction target traveling course Rc2,
instead of maintaining the target speed at 60 km/h, the target speed is gradually
reduced as the vehicle 1 approaches the vehicle 3, and then gradually increased to
60 km/h as the original vehicle speed, as the vehicle 1 travels away from the vehicle
3.
[0091] The correction to be achieved by changing only the target speed without changing
the target positions of the target traveling course R, as in the post-correction target
traveling course Rc1, can be applied to a driving support mode which involves the
speed control but does not involve the steering control (e.g., the automatic speed
control mode, the speed limiting mode, and the basic control mode).
[0092] Further, the correction to be achieved by changing only the target positions without
changing the target speed of the target traveling course R, as in the post-correction
target traveling course Rc3, can be applied to a driving support mode which involves
the steering control (e.g., the preceding vehicle following mode).
[0093] Further, the correction to be achieved by changing both the target positions and
the target speed of the target traveling course R, as in the post-correction target
traveling course Rc2, can be applied to a driving support mode which involves the
speed control and the steering control (e.g., the preceding vehicle following mode).
[0094] Subsequently, the control part 10f comprised in the ECU 10 operates to determine
an optimal corrected traveling course from among the corrected traveling course candidates
settable as a corrected traveling course, based on sensor information and others.
Specifically, the control part 10f operates to determine an optimal corrected traveling
course from among the corrected traveling course candidates, based on the given evaluation
function and the given limiting condition.
[0095] The ECU10 stores the evaluation function J, the limiting condition and a vehicle
model in the memory. For determining an optimal corrected traveling course, the control
part 10f is operable to calculate, as the optimal corrected traveling course, one
of the corrected traveling course candidates, which has an extreme value in terms
of the evaluation function J, while satisfying the limiting condition and the vehicle
model (optimization processing).
[0096] The evaluation function J has a plurality of evaluation factors. In this embodiment,
the evaluation factors are a function for evaluating the adequacy of a plurality of
corrected traveling course candidates obtained by correcting the target traveling
course, in terms of, e.g., speed (longitudinal and lateral speeds), acceleration (longitudinal
and lateral accelerations), acceleration change rate (longitudinal and lateral acceleration
change rates), yaw rate, lateral offset with respect to the widthwise middle of a
lane, vehicle angle, steering angle, and other software limitations.
[0097] The evaluation factors include an evaluation factor regarding a longitudinal behavior
of the vehicle 1 (longitudinal evaluation factor: longitudinal speed, longitudinal
acceleration, longitudinal acceleration change rate, etc.), and an evaluation factor
regarding a lateral behavior of the vehicle 1 (lateral evaluation factor: lateral
speed, lateral acceleration, lateral acceleration change rate, yaw rate, lateral offset
with respect to the widthwise middle of a lane, vehicle angle, steering angle, etc.).
[0098] In this embodiment, the evaluation function J is expressed as the following formula:
[0099] In this formula, Wk (Xk - Xrefk)
2 denotes each of the evaluation factors, wherein: Xk denotes a physical value of the
corrected traveling course candidate in regard to each of the evaluation factors;
Xrefk denotes a physical value of the target traveling course (before correction)
in regard to a corresponding one of the evaluation factors; and Wk denotes a weighting
factor for the corresponding one of the evaluation factors (e.g., 0 ≤ Wk ≤ 1) (where
k is an integer of 1 to n). Thus, in this embodiment, the evaluation function J is
equivalent to a value obtained by: calculating differences in respective physical
amounts of n evaluation factors between a corrected traveling course candidate and
a target traveling course (before correction); weighting respective square values
of the differences; and summing the weighted values over a traveling course distance
corresponding to a given time period N (e.g., N = 3 sec).
[0100] In this embodiment, the evaluation function J has a smaller value as a corrected
traveling course candidate obtained by correcting the target traveling course has
a higher evaluation. That is, among the plurality of corrected traveling course candidates,
one corrected traveling course candidate having a minimum value in terms of the evaluation
function J is calculated as an optimal corrected traveling course by the control part
10f.
[0101] The limiting condition is a condition to be satisfied by each of the corrected traveling
course candidates. Thus, the corrected traveling course candidates to be evaluated
can be narrowed down by the limiting condition, so that it is possible to reduce a
computational load necessary for the optimization processing based on the evaluation
function J, thereby shortening a computational time period.
[0102] The vehicle model is designed to define physical motions of the vehicle 1, and expressed
as the following motion equations. In this embodiment, this vehicle model is a two-wheel
vehicle model as shown in FIG. 8. The physical motions of the vehicle 1 can be defined
by the vehicle model, so that it is possible to calculate a corrected traveling course
which is less likely to give a driver a feeling of strangeness during traveling, and
early converge the optimization processing based on the evaluation function J.
[0103] In FIG. 8 and the equations (3) and (4), m denotes a mass of the vehicle 1; I denotes
a yawing inertia moment of the vehicle 1; 1 denotes a wheelbase of the vehicle 1;
l
f denotes a distance between a center-of-gravity and a front axle of the vehicle 1;
l
r denotes a distance between the center-of-gravity and a rear axle of the vehicle 1;
K
f denotes a cornering power per front road wheel of the vehicle 1; K
r denotes a cornering power per rear road wheel of the vehicle 1; V denotes a vehicle
speed of the vehicle 1; δ denotes an actual steering angle of a front road wheel of
the vehicle 1 ; β denotes a lateral slip angle at the center-of-gravity; r denotes
a yaw angular speed of the vehicle 1; θ denotes a yaw angle of the vehicle 1; y denotes
a lateral displacement with respect to an absolute space; and t denotes time.
[0104] In this way, the control part 10f is operable, based on the target traveling course,
the limiting condition, the vehicle model, etc., to calculate an optimal corrected
traveling course which is the smallest in terms of the evaluation function J, from
among the plurality of corrected traveling course candidates.
[0105] Next, with reference to FIGS. 9 to 13, a flow of vehicle control processing in the
vehicle control device 100 according to this embodiment will be described. FIG. 9
is a flowchart of a driving support control processing routine, and FIG. 10 is a flowchart
of speed limit distribution setting processing.
[0106] The ECU 10 operates to repeatedly execute a processing routine according to the flowchart
in FIG. 9, at intervals of a given time period (e.g., 0.1 sec). First of all, the
input processing part 10a of the ECU 10 operates, in step S10, to execute data reading
as information acquisition processing. In the information acquisition processing,
the ECU 10 operates to acquire the current vehicle position information, the map information,
information regarding the surrounding object, and the like, from the position measurement
system 24, the navigation system 25 and the inter-vehicle communication system 26,
and acquire the sensor information from the camera 21, the millimeter-wave radar 22,
the vehicle speed sensor 23 and others. Here, the ECU 10 may be configured to acquire
additional sensor information from an acceleration sensor, a yaw rate sensor, the
driver manipulation unit (which are not shown) and others. Further, the ECU 10 may
be configured to acquire switch information from a steering angle sensor, an accelerator
position sensor, a brake sensor (which are not shown) and others.
[0107] The ECU 10 also operates to detect vehicle manipulation information regarding vehicle
manipulation by a driver (steering angle, accelerator pedal depression amount, a brake
pedal depression amount, etc.) from the switch information, and further detect traveling
behavior information regarding the behavior of the vehicle 1 (vehicle speed, longitudinal
acceleration, lateral acceleration, yaw rate, etc.).
[0108] Here, information received from a surrounding vehicle via the inter-vehicle communication
system 26 includes the traveling position, attitude angle, traveling speed, steering
angle, accelerator pedal depression amount, brake pedal depression amount and others
of the surrounding vehicle, as information regarding a traveling state of the surrounding
vehicle. Further, in a case where the surrounding vehicle is equipped with a vehicle
control device such as a driving support device or an automatic driving device, information
regarding a traveling course in a time period subsequent to the present time, set
in the vehicle control device of the surrounding vehicle, is also received via the
inter-vehicle communication system 26.
[0109] Subsequently, the ECU 10 operates, in step S11, to execute given object detection
processing, using the variety of information acquired through the information acquisition
processing. In the object detection processing, the ECU 10 operates to detect, based
on the current vehicle position information, the map information, the information
from the inter-vehicle communication system 26 and the sensor information, traveling
road information regarding the shape of a traveling road in areas around and forward
of the vehicle 1 (the presence or absence of a straight section and a curve section,
the length of each of the straight and curve sections, the curvature radius of the
curve section, a lane width, the positions of opposed lane edges, the number of lanes,
the presence or absence of an intersection, a speed limit determined by the curvature
of the curve section, etc.), traveling regulation information (legal speed limit,
red light, etc.), and the preceding vehicle trajectory information (traveling trajectory
of a preceding vehicle). As the object detection processing, the surrounding vehicle
detection part 10b of the ECU 10 operates to detect, based on the information from
the inter-vehicle communication system 26 and the sensor information from the camera
21 and the like, surrounding object information regarding a surrounding object including
a surrounding vehicle (the presence or absence, type, size, position, etc., of an
obstacle on a traveling courser). Thus, the processings in the steps S10 and S11 serve
as an information receiving step of detecting a surrounding vehicle traveling around
the own vehicle, and receiving, from the detected surrounding vehicle, manipulation
information regarding acceleration/ deceleration and/or steering by a driver of the
surrounding vehicle 3, and information regarding the road surface condition, via the
inter-vehicle communication system 26.
[0110] Subsequently, the speed distribution setting part 10e of the ECU 10 operates, in
step S12, to execute speed limit distribution setting processing. Specifically, the
speed distribution setting part 10e operates to set the speed limit distributions
40 illustrated in FIG. 6, around a surrounding object such as a surrounding vehicle
detected in the step S11 by the surrounding vehicle detection part 10b. Thus, the
processing in the step S12 serves as a speed distribution setting step of setting,
around the surrounding vehicle 3, the speed limit distributions 40 each defining a
permissible upper limit relative speed.
[0111] Subsequently, in step S13, the target traveling course calculation part 10c of the
ECU 10 operates to calculate the target traveling courses illustrated in FIGS. 3 to
5, using the traveling road information detected in the step S11. Further, the control
part 10f operates to correct a selected one of the calculated target traveling courses
to satisfy the speed limit distributions 40, thereby calculating a corrected traveling
course defining a traveling trajectory and a traveling speed appropriate to the traveling
trajectory.
[0112] Subsequently, the control part 10f of the ECU 10 operates, in step S14, to output
a request signal to each of one or more control systems concerned (the engine control
system 31, the brake control system 32 and/or the steering control system 33) so as
to allow the own vehicle to travel on the corrected traveling course calculated in
the step S13. Specifically, the ECU 10 operates to generate a request signal according
to a target control amount of each of the engine, brake and steering, determined by
the calculated corrected traveling course, and output the generated request signal.
Thus, the processings in the steps S13 and S14 serves as a control step of controlling
speed and/or steering of the own vehicle to satisfy the set speed limit distributions.
[0113] Next, with reference to FIGS. 10 to 13, the speed limit distribution setting processing
to be executed in the step S12 of the flowchart illustrated in FIG. 9 will be described.
[0114] FIG. 10 is a flowchart of the speed limit distribution setting processing to be executed
as a subroutine of the flowchart illustrated in FIG. 9. FIG. 11 is an explanatory
diagram of estimation of the road surface µ of a traveling road surface, based on
a traveling state of a surrounding vehicle. FIG. 12 is a graph showing a change in
the permissible upper limit relative speed under the condition that the road surface
µ on which the surrounding vehicle is traveling is relatively low, and FIG. 13 is
a diagram showing a change in the speed limit distributions under this condition.
[0115] First of all, in step S21 of FIG. 10, the road surface condition estimation part
10d operates to estimate the road surface condition, based on the information regarding
the road surface condition the surrounding vehicle 3 traveling forward of the own
vehicle 1, acquired via the inter-vehicle communication system 26 in the step S10
of FIG. 9. The road surface condition to be estimated is one factor exerting an influence
on the braking distance by the brake of the own vehicle 1. In this embodiment, a road
surface µ (friction coefficient of a road surface) of the lane in which the own vehicle
1 is traveling is estimated.
[0116] Here, the inter-vehicle communication system 26 is configured to repeatedly receive,
from a surrounding vehicle traveling or parked around the own vehicle 1, the information
regarding the traveling state of the surrounding vehicle 3, at intervals of a given
time period. This time interval is sufficiently short. Thus, for example, based on
the traveling state of a preceding vehicle (surrounding vehicle 3) traveling in the
lane of the own vehicle 1, it is possible to continuously estimate the road surface
µ of a road surface on which the own vehicle 1 will subsequently travel, and early
figure out a forward road surface condition.
[0117] FIG. 11 is an explanatory diagram of estimation of the road surface µ. As shown in
FIG. 11, the surrounding vehicle 3 traveling forward of and in the lane of the own
vehicle repeatedly transmits information regarding the traveling position, vehicle
attitude angle, traveling speed, steering wheel turning angle, etc., of the surrounding
vehicle 3 via the inter-vehicle communication system 26. The transmitted information
regarding the traveling state of the surrounding vehicle 3 is received by the own
vehicle 1 via the inter-vehicle communication system 26. The road surface condition
estimation part 10d operates to calculate a traveling trajectory R of the surrounding
vehicle 3, based on the traveling position of the surrounding vehicle 3 received via
the inter-vehicle communication system 26. Further, the road surface condition estimation
part 10d operates to calculate a centrifugal force acting on the surrounding vehicle
3, based on the traveling speed of the surrounding vehicle 3 received via the inter-vehicle
communication system 26, and a curvature radius of the traveling trajectory R. This
centrifugal force is balanced with a lateral force generated between a tire of the
surrounding vehicle 3 and the road surface. Thus, the lateral force F
1 of the surrounding vehicle 3 can be calculated.
[0118] Further, the road surface condition estimation part 10d operates to calculate a slip
angle β
r of a rear road wheel of the surrounding vehicle 3, based on the vehicle attitude
angle of the surrounding vehicle 3 received via the inter-vehicle communication system
26. Specifically, the slip angle β
r of the rear road wheel can be computed as an angle between a tangent line R
t to the traveling trajectory R of the surrounding vehicle 3 and a longitudinal axis
line C of the surrounding vehicle 3. A steering angle of a front road wheel of the
surrounding vehicle 3 can also be calculated, based on the received steering wheel
turning angle of the surrounding vehicle 3, and then a slip angle β
f of the front road wheel can be computed based on the calculated steering angle.
[0119] Based on the lateral force F
1 of the surrounding vehicle 3, the slip angle β
r of the rear road wheel of the surrounding vehicle 3 and the slip angle β
f of the front road wheel of the surrounding vehicle 3 obtained in the above manner,
the road surface µ of the road surface on which the surrounding vehicle 3 is traveling
can be estimated. Specifically, in a situation where the surrounding vehicle 3 is
traveling on a road surface having a high road surface µ, the slip angle β
r or β
f is relatively small with respect to the lateral force Fi, as shown in the left side
of FIG. 11. On the other hand, in a situation where the surrounding vehicle 3 is traveling
on a road surface having a low road surface µ, the slip angle β
r or β
f is relatively large with respect to the lateral force Fi, as shown in the left side
of FIG. 11. As above, when the road surface µ is high, a relatively large lateral
force F
1 is generated at a relatively low slip angle β
r or β
f, but when the road surface µ becomes lower, the slip angle β
r or β
f necessary to generate the same lateral force F
1 becomes larger.
[0120] The road surface condition estimation part 10d operates to estimate, based on such
a relationship, the road surface µ of the road surface on which the surrounding vehicle
3 is traveling. For example, it is known that; a normal paved road has a road surface
µ of about 1.0; a normal paved road, a frozen road has a road surface µ of about 0.1;
and a snowy road has a road surface µ of about 0.3 to 0.5. In this embodiment, the
road surface µ is estimated by acquiring the traveling position, vehicle attitude
angle, traveling speed, steering wheel turning angle and others of the surrounding
vehicle 3, via the inter-vehicle communication system 26. Alternatively, a part or
the entirety of the above information may be calculated based on information from
the millimeter-wave radar 22, the camera 21 and the like equipped in the own vehicle
1, without the intermediary of the inter-vehicle communication system 26.
[0121] Subsequently, in step S22 of FIG. 10, it is determined whether or not the value of
the road surface µ estimated by the road surface condition estimation part 10d is
equal to or less than a given value. When the road surface µ is determined to be equal
to or less than the given value, the steps S23 and S24 will be sequentially executed.
On the other hand, when it is determined to be greater than the given value, the step
S24 will be executed. For example, when the value of the estimated road surface µ
is equal to or less than 0.5, it is determined that the road surface µ is small or
low.
[0122] When the road surface µ is determined to be equal to or less than the given value,
the subroutine proceeds to the steps S23 in which the value of the correction coefficient
β of the formula (2) for calculating the permissible upper limit relative speed V
lim is changed. Here, at the time when the subroutine of the flowchart illustrated in
FIG. 10 is started, default values of the correction coefficients are set as follows:
α = 1, and β = 1. That is, in this embodiment, as shown in the left graph of FIG.
12, during traveling on a normal road surface (road surface having a high road surface
µ), the correction coefficient β is 1, so that the permissible upper limit relative
speed V
lim quadratically increases along with an increase in the distance Y to the surrounding
vehicle. On the other hand, when the road surface µ of the road surface on which the
forward surrounding vehicle 3 is traveling is estimated to be low, the correction
coefficient β is changed to 0.8. Thus, as shown in the right graph of FIG. 12, a slope
at which the permissible upper limit relative speed V
lim quadratically increases along with an increase in the distance Y is changed to become
gentler.
[0123] As above, the road surface condition estimation part 10d operates to estimate the
state of the traveling road surface of the surrounding vehicle 3, based on the manipulation
information received via the inter-vehicle communication system 26. When the estimated
road surface µ is equal to or less than the given value, the road surface condition
estimation part 10d operates to determine that the road surface condition causes an
increase in the braking distance as compared to a normal state, and then lower the
permissible upper limit relative speed. In this embodiment, when the road surface
µ is greater than the given time, and the information regarding the traveling road
surface of the surrounding vehicle 3 cannot be obtained, such a state is regarded
as "normal state", and the correction coefficient β is kept at the default value "1".
[0124] After setting the value of the correction coefficient β in the step S23, the subroutine
in the ECU 10 proceeds to step S24. In the step S24, the speed distribution setting
part 10e operates to set the speed limit distributions 40, based on the set values
of the correction coefficients α, β (α is kept at the default value). Then, one cycle
of the subroutine in the flowchart of FIG. 10 is completed, and the subroutine returns
to the flowchart of the FIG. 9.
[0125] In the step S23, the correction coefficient β is changed to a smaller value, so that
the speed limit distributions 40 set in the step S24 are changed from a pattern illustrated
on the left side of FIG. 13 to a pattern illustrated on the right side of FIG. 13.
Specifically, the speed limit distributions 40 are set such that the permissible upper
limit relative speed becomes higher as the distance from the surrounding vehicle 3
becomes larger. Then, the speed limit distributions 40 are changed from a pattern
for the high road surface µ, i.e., in the normal state, as illustrated on the left
side of FIG. 13, to a pattern expanded rearwardly in the traveling direction from
the surrounding vehicle 3, as illustrated on the right side of FIG. 13. In this way,
when the traveling road surface of the surrounding vehicle 3 traveling forward of
the own vehicle 1 is estimated to have a low road surface µ, the speed limit in each
of the speed limit distributions 40 is lowered in the traveling direction. That is,
when it is estimated by the road surface condition estimation part 10d that the road
surface condition causes an increase in the braking distance, the permissible upper
limit relative speed is lowered with respect to the distance from the surrounding
vehicle 3. Here, even in a situation where the road surface µ is low, the value of
the correction coefficient α of the formula (1) is not changed. Thus, the width of
each of the speed limit distributions 40 in the lateral direction (which is orthogonal
to the traveling direction of the own vehicle) is the same as that in the normal state.
[0126] In the example illustrated in FIG. 13, when the own vehicle 1 is traveling at a position
apart rearwardly from the surrounding vehicle 3 by a distance Y1, no speed limit is
set on the own vehicle in the normal state (when the road surface µ is high), as illustrated
on the left side of FIG. 13. On the other hand, when the traveling road surface of
the surrounding vehicle 3 is estimated to have a low road surface µ, and then the
correction coefficient β is changed to 0.8, the own vehicle 1 enters inside a distribution
line of the permissible upper limit relative speed "60 km/h", as illustrated on the
right side of FIG. 13, so that the relative speed is limited to 60 km/h. In this way,
in the situation where the road surface on which the surrounding vehicle 3 is traveling
is estimated to have a low road surface µ, the braking distance of the own vehicle
1 is increased. Thus, the permissible upper limit relative speed is lowered with respect
to the same distance Y from the surrounding vehicle 3.
[0127] As above, in this embodiment, when the road surface on which the forward surrounding
vehicle 3 is traveling is estimated to have a low road surface µ, the permissible
upper limit relative speed is lowered, so that it is possible to early limit the relative
speed in a state in which the own vehicle 1 is traveling sufficiently away from the
surrounding vehicle 3, thereby sufficiently safely stop the own vehicle 1 even if
the braking distance of the own vehicle 1 is increased. This makes it possible to
reduce a feeling of insecurity to be given to a driver, even in the situation where
the road surface condition causes an increase in the braking distance of the own vehicle
1.
[0128] On the other hand, when the road surface is determined, in the step S24 of FIG. 10,
not to have a low road surface µ, the subroutine proceeds to the step S25. In this
case, the speed distribution setting part 10e operates, in the step S24, to set the
speed limit distributions 40, based on the set corrected coefficients α, β (both α
and β are kept at the default values). Then, one cycle of the subroutine in the flowchart
of FIG. 10 is completed, and the subroutine returns to the flowchart of the FIG. 9.
[0129] As above, in this embodiment, when the road surface on which the forward surrounding
vehicle 3 is traveling is estimated to have a low road surface µ, the permissible
upper limit relative speed is lowered, and thereby, with respect to the same relative
speed, a longer inter-vehicle distance is set between the own vehicle 1 and the surrounding
vehicle 3. Thus, even in the situation where the braking distance of the own vehicle
1 is increased, it is possible to avoid an accidental approach between the own vehicle
1 and the surrounding vehicle 3, thereby reducing a feeling of insecurity to be given
to a driver.
[0130] In the vehicle control device 100 according to the above embodiment, when the road
surface condition is estimated to cause an increase in the braking distance, the permissible
upper limit relative speed is lowered (FIG. 13), so that it is possible to increase
a permissible inter-vehicle distance with respect to the same relative speed, thereby
suppressing a feeling of insecurity to be given to a driver.
[0131] In the vehicle control device 100 according to the above embodiment, the information
regarding the traveling state of the surrounding vehicle 3 is received from the surrounding
vehicle 3, and it is estimated, using the received information, whether or not the
road surface condition causes an increase in the braking distance, so that it is possible
to finely estimate the road surface condition and adequately set the speed limit distributions
40. Further, the road surface condition is estimated using the information regarding
the traveling state transmitted from the surrounding vehicle 3, so that it is possible
to estimate not only the state of a road surface on which the own vehicle 1 is currently
traveling, but also the state of a forward road surface on which the own vehicle 1
will subsequently travel, thereby early coping with a situation where the forward
road surface condition changes.
[0132] In the vehicle control device 100 according to the above embodiment, the road surface
condition estimation part 10d operates to estimate the road surface µ of a traveling
lane, and determine, based on the estimated road surface µ, whether or not the road
surface condition causes an increase in the braking distance, so that it is possible
to estimate the braking distance by a simple method. Further, when the road surface
condition is estimated to cause an increase in the braking distance, the permissible
upper limit relative speed in the traveling direction is lowered, so that it is possible
to ensure sufficient safety even when the braking distance is increased.
[0133] In the vehicle control device 100 according to the above embodiment, when the road
surface condition is estimated to cause an increase in the braking distance, the permissible
upper limit relative speed is lowered with respect to the distance from the surrounding
vehicle (FIG. 13), and thereby a traveling directional distance between the surrounding
vehicle 3 and the own vehicle 1 is increased with respect to the same relative speed,
so that it is possible to sufficiently give a driver a feeling of security even in
the road surface condition causing an increase in the braking distance.
[0134] Although the present invention has been described based on a preferred embodiment
thereof, it should be understood that various changes and modifications may be made
therein. Particularly, in the above embodiment, information is received from the surrounding
vehicle 3 traveling forward of the own vehicle 1 via the inter-vehicle communication
system 26, and it is determined, based on the received information, whether or not
the road surface exerts an influence on braking distance by the brake of the own vehicle
1. As one modification, the vehicle control device of the present invention may be
configured to determine whether or not the road surface exerts an influence on the
braking distance, without estimating the road surface µ. For example, the road surface
condition causing an increase of the braking distance may be estimated by detecting
rainy weather using a wiper sensor equipped in the own vehicle 1, or by detecting
a possibility of road surface freezing based on the fact that an ambient temperature
measured by an ambient temperature sensor is 0°C or less. In this case, the road surface
condition estimation part 10d is configured to estimate the road surface condition
exerting an influence on the braking distance, based on a detection value of the wiper
sensor or the ambient temperature sensor.
[0135] Further, in the above embodiment, when the road surface µ of the traveling road surface
of the forward surrounding vehicle 3 is equal to or less than the given value, the
correction coefficient β is lowered from 1 to 0.8 in a stepwise manner (the step S23
of FOG. 10). As one modification, the correction coefficient β may be linearly reduced,
as shown in FIG. 14. Specifically, in this modification, in the normal state (when
the road surface µ is high), the correction coefficient β is 1, and, when the road
surface µ of the traveling road surface becomes less than a given value µ
1 (becomes less than a given friction coefficient µ
1), the correction coefficient β is linearly changed to a smaller value. Preferably,
when the road surface µ of the traveling road surface becomes less than a given value
µ
1 of 0.5, the correction coefficient β starts to be reduced, and linearly reduced to
about 0.5 for a frozen road having an extremely low road surface µ.
LIST OF REFERENCE SIGNS
[0136]
- 1:
- vehicle
- 10:
- vehicle control and computing unit (ECU)
- 10a:
- input processing part
- 10b:
- surrounding vehicle detection part
- 10c:
- target traveling course calculation part
- 10d:
- road surface condition estimation part
- 10e:
- speed distribution setting part
- 10f:
- control part
- 21:
- camera
- 22:
- millimeter-wave radar
- 23:
- vehicle speed sensor
- 24:
- position measurement system
- 25:
- navigation system
- 26:
- inter-vehicle communication system (vehicle information receiving part)
- 31:
- engine control system
- 32:
- brake control system
- 33:
- steering control system
- 40:
- speed limit distribution
- 100:
- vehicle control device